The invention is directed to a process for the production of suspension polymerizates by polymerization of esters of acrylic acid or methacrylic acid or vinyl aromatics, or monomer mixtures which predominantly consist of such monomers, in aqueous suspension and in the presence of a homopolymerizate of acrylic acid or methacrylic acid or a copolymerizate which is derived from at least 50 percent by weight of acrylic acid or methacrylic acid, in the form of the free acid or its alkali metal (e.g. sodium or potassium) or ammonium salt.
The suspension polymerization of esters of acrylic acid or methacrylic acid or vinyl aromatics or monomer mixtures which predominantly consist of such monomers is basically known.
It is also known to use as dispersing agents in such polymerization homopolymers of acrylic acid or methacrylic acid or copolymerizates which are derived from at least 50 percent by weight of these acids. These polymerizates can be used in the form of the free acids or as alkali metal or ammonium salts. They have the advantage that they are generally easy to remove through washing the polymerizate beads which are formed. However, less satisfactory is the fact that the customary procedures for controlling the average size of the beads, such as variations in the number of revolutions per minute of the stirrer and/or the amount of dispersing agent have little effect in using these polymerizates. Especially it is difficult to produce relatively large beads (average diameter about 0.3 to 1 mm), since with too great a reduction of the speed of rotation of the stirrer and/or the amount of dispersing agent the stability of the suspension is no longer guaranteed.
However, the formation of relatively coarse beads is frequently very desirable because they are easier to separate from the aqueous suspension than fine beads and as a rule because of their lower specific surface area contain less impurities.